Gravity Flows in Late Quaternary Sediments in Northwestern Russia (Kola Region) and Their Possible Relationship with Pleistocene Earthquakes

The lithological features of Late Quaternary sediments deposited during the marine isotope stage (MIS) 3 in the Ura River valley on the Barents Sea coast (Kola region, northwestern Russia) have been studied. Seismo-induced soft-sediment deformation structures (SSDS) are preserved in the sandy–clayey deposits as five deformed layers separated by undisturbed deposits. These layers are marked by load casts, flame structures, injections, sedimentary breccia, and folds. The SSDS were produced by several processes: origination of debris flows in the subaqueous setting due to shear stress, gravity load of the overlying deposits, and liquefaction. The seismic shock and aftershocks could trigger the gravity flow activity and initiate the processes of liquefaction and fluidization of sediments. We believe that the main seismogenic zone was related to reactivation of the large Karpinsky oblique-slip fault, which separated the Baltic Shield from the Barents Sea Plate of the West Arctic Platform, contrast movements at the boundary of large structural elements, and development of strains at the front of the advancing Weichselian Ice Sheet at MIS 2.